Phosphatidylserine decarboxylases (PSDs) catalyze the production of phosphatidylethanolamine (PE) from phosphatidylserine (PS) and are crucial for the maintenance of PE levels in fungi. The PSDs are classified into two types; the type I PSDs are conserved from bacteria to humans, while the type II PSDs exist only in fungi and plants. In yeasts, the deletion of type I PSD-encoding genes causes severe growth retardation. In contrast, the deletion of type II PSD-encoding genes has little or no effect. In this study, we found four genes encoding type II PSD orthologs in the filamentous fungus Aspergillus nidulans; these included psdB, psdC, psdD, and psdE. Deletion of psdB caused severe growth defects on minimal medium and these defects were partially restored by the addition of ethanolamine, choline, PE, or phosphatidylcholine into the medium. The conidiation efficiency of the psdB deletion mutant was dramatically decreased and its conidiophore structures were aberrant. In the psdB deletion mutant, the PE content decreased while the PS content increased. We further showed that PsdB had a major PSD activity. Our findings suggest that the type II PSDs exert important roles in the phospholipid homeostasis, and in the growth and morphogenesis of filamentous fungi. (C) 2020, The Society for Biotechnology, Japan. All rights reserved.